More than twice as many heads are working well into their sixties than five years ago, it has emerged.
Figures released by the General Teaching Council for Wales show that 132 on its register are 60 or over; five are over 65. For the first time, no head is under 30, while 65 per cent are now aged 50 or over.
Heads' unions voiced concern but said the latest figures were not surprising. Iwan Guy, acting director of the National Association of Head Teachers Cymru and a former primary head, said he knew heads who had sacrificed retirement as suitable replacements could not be found, especially for those in Welsh-medium schools.
Gareth Jones retired as head of Ysgol Derwen Primary in Flintshire last year, aged 60. A replacement was found quickly, but he said he would have continued until another head was found. "Other schools are in a situation where governing bodies cannot find heads and existing ones stay on rather than retire," he said. "It is telling that there were only six candidates for my job, compared with 80 when I was appointed in 1986."
Assembly government figures show there were seven head and deputy vacancies at the end of 2007 in Wales. All but one - a Welsh-medium post - was filled; 22 per cent of head vacancies now have to be readvertised in Wales.
Heads say the job has changed so much that assistant heads are loath to step up. They say that while the workforce deal has cut teachers' burden, heads' workload has increased.
Despite a high turnover of secondary heads expected over the next five years as many reach retirement age, the number of applicants is falling. The teaching council's figures also show that a growing number of heads now have the National Professional Qualification for Headship: 436 in 2008.
Gareth Jones, former head and secretary of the Association of School and College Leaders, said: "We need to make it more attractive for people to apply for headships and make deputy and assistant heads feel inclined to do the NPQH."
Alma Harris, professor of educational leadership at London's Institute of Education, said the statistics showed an "urgent need to repopulate the leadership pool" in Wales.
Education minister Jane Hutt has promised more action and money to tackle the problem, but said the recruitment crisis was not as acute in Wales as in England.
1,751 - Total number of heads in Wales in 2008
52.5 - Percentage of all heads in Wales who are female
84 - Percentage of secondary heads in Wales who are male.